Temperatures are expected to plummet as low as -15C in parts of the UK over the coming days as several inches of snowfall threatens to block roads and railways.
Even London could see light snow as the cold snap takes hold, bringing ice, frost and Arctic winds to the country.
Amber and yellow warnings are in place on Wednesday and Thursday in parts of northern England and Scotland, with the heaviest snow arriving in Shetland and border regions tonight.
The Met Office is urging people to prepare for “very difficult travelling conditions” and possible disruption to transport and power supplies, while cold alerts have been issued by Public Health England and charities for asthma sufferers and the elderly.
Most places are already feeling colder and it was a chilly night last night,” she said.
“A band of light rain is spreading east and those showers will turn to snow across the north.
“Lower ground could see 3-6cm, while higher ground could have up to 10cm, which will make for some tricky conditions up there.
“Elsewhere, showery rain will be moving eastwards across England and Wales, with quite heavy bursts of rain for a time.”
As the cold air sinks southwards on Thursday, the rain could turn into wintery showers and the “odd flake of snow” that will be unlikely to settle across central England.
“In other places it will be dry and mostly cold, with a sharp overnight frost,” Ms Sharples said.
“It’s possible that there will be a few flakes coming down in London but it’s more likely to be further north.
“Through the weekend it will get even colder. Saturday night into Sunday looks to be the coldest.
“It will depend on how much snow is lying but I suspect temperatures into the double figures negative, between -10 and -15C in remote areas of Scotland.
“Places without snow will be just below freezing -5C will be seen fairly widely, which is a change from what we’ve been seeing.”
The sub-zero temperatures come after the warmest December on record, which was also one of the wettest ever with a succession of storms that devastating floods.
Officials have urged families to help protect their relatives from the sudden cold snap.
Dr Angie Bone, head of protection at Public Health England, said: “Over the past few weeks we’ve had some very disruptive weather, but temperatures have been quite mild – now the weather will be colder over much of the country, which will be a significant change.
“It’s so important to remember that cold does kill, even in places where the temperatures aren’t at their lowest. Most of our advice at PHE on keeping warm in cold weather may seem like common sense but people should think about how the cold weather can affect them.”
Homes should be heated to at least 18C and the elderly and anyone suffering from a cold-affected condition should have plenty of hot drinks and get a flu vaccination if they are eligible, she said.
Additional reporting by PA